In the provision of wireless communication services within a cellular network, individual geographic areas or “cells” are defined and serviced by base stations. A base station typically has a cellular tower and utilizes RF antennas that communicate with wireless devices, such as cellular phones and pagers. The base stations are linked with other facilities of the service provider, such as a switching or central office, for handling and processing the wireless communication traffic.
A base station may be coupled to a processing facility through cables or wires, referred to as land lines, or alternatively, the signals may be transmitted or backhauled through microwave backhaul antennas, also located on the cellular tower and at the facility. Backhauls may be used in situations where land lines are unavailable or where a service provider faces an uncooperative local carrier and wants to ensure independent control of the circuit. In such a scenario, the backhaul may be referred to as a point-to-point backhaul, referencing the base station and the processing facility as points.
Point-to-point backhauls, are currently being deployed in the unlicensed spread spectrum bands, (e.g. Industrial, Scientific, and Medical (ISM) band covering 902-928 MHz, Unlicensed National Information Infrastructure band (U-NII) at 5.15-5.25 GHz, 5.25-5.35 GHz, and 5.725-5.825 GHz, etc.), to avoid the cost and time delays associated with installation in licensed frequency bands. One type of antenna that may be used for point-to-point backhauls utilizes a parabolic dish that is mounted to a tower, a wall, a building or in another location, and aimed at the other point in the backhaul. Parabolic dishes are sometimes unsightly and spoil the aesthetic appearance of the location where they are mounted.
Another type of antenna that may be used for point-to-point backhauls is a planar antenna array. Planar antenna arrays may also be mounted to a tower, a wall or a building, with the antenna being electrically pointed, i.e., via beamsteering, at the other point in the backhaul. Planar antenna arrays are generally thought of as more aesthetically appealing than parabolic dishes. Moreover, beamsteering makes planar antenna arrays more desirable in reconfiguring a cellular network. However, planar antenna arrays generally suffer from a variety of limitations.
For instance, planar antennas arrays tend to be constructed using arrays of patch radiating elements. In order to form these elements and ease manufacturing, planar antennas may be constructed using printed circuit boards. However, these boards often utilize multiple layer construction techniques in order to form the elements and the feed networks used therewith. Such construction increases the cost of such boards.
Moreover, planar antennas constructed using arrays of patch radiating elements formed using multiple layer circuit boards typically use corporate feed networks for coupling the elements in the arrays. Such corporate feed networks are often in the form of microstrip or twin-lead feed lines deposited on one or more layers of a circuit board. Such corporate feed networks typically have high losses, while such microstrip or twin-lead feed lines typically result in poor cross-polarized performance of an antenna.
In addition, the use of multiple layer circuit boards may economically and/or practically limit the size of the antenna. For example, current production capabilities of circuit board suppliers, along with the production costs associated with constructing a circuit board larger than currently available, limit the size of multiple layer circuit boards. Further, techniques of coupling two or more circuit boards together, thereby realizing a larger circuit board, are largely thwarted as interconnection of multiple conductive layers in each board tends to be impractical. Due to these economic and practical limitations in the size of circuit boards available, planar antennas constructed using such circuit boards may be limited in aperture size, i.e., the distance between the outer two most arrays of elements in an antenna, which determines in part the ability to electrically point the antenna.
Thus, these limitations typically associated with planar antennas may reduce antenna performance, efficiency and increase amplification requirements, and may limit the ability to electrically point such an antenna.
Therefore, a need exists for a low cost, low loss, large aperture planar antenna having an improved front-to-back ratio and cross-polarized performance with reduced susceptibility to other sources of radiation for applications such as a point-to-point microwave backhaul.